Australia's world No.9 de Minaur advanced when his semi-final opponent Jack Draper retired during the third set on Friday (Saturday AEDT).

De Minaur won the first set 6-3, dropped the second 6-2 and was leading 4-0 in the third when Englishman Draper, who was visibly diminished physically, called it quits.

The third seed will battle for the title with Ruud, who pulled off an upset by beating second-seed Holger Rune 3-6 6-3 6-4 in the second semi.

It will be Ruud's second final in the country in as many weeks, but he will hope for a better result on Saturday after losing in Los Cabos to another Australian, Jordan Thompson.

The 25-year-old de Minaur won his ninth straight match in Mexico and became the first defending champion to reach the Acapulco final since David Ferrer in 2013.

"I'm happy to be in the final, but I'm hoping that Jack is doing fine. He has a tremendous talent and hopefully he can recover for the upcoming tournaments," de Minaur said.

"It's hard to play when your opponent is not OK physically, but you need to remain focused."

De Minaur has seven career ATP titles, with last year at Acapulco his most recent.

Draper was playing in his first semi-final of an ATP 500 tournament.

In the other semi, Ruud lost the first set and then was down 3-1 in the third with Rune serving, but he managed a couple of breaks and held his serve to take the win.

"I'm like a cockroach, not going anywhere, just creeping back in," Ruud joked when asked about his about his ability to respond after seemingly getting knocked down.

"I did not get the best start, and the third set looked really bad, I just tried to stay in there and it seemed like Holger was struggling and at the end it worked for me," said Ruud.

The 25-year-old Norwegian will try to win his 10th career title, the first one on a ATP 500.

Rune, who is the seventh player on the ATP rankings, lost in the Acapulco semi-finals for the second year in a row.

Australian Associated Press